In oil and gas perforating operations, much greater penetration is achieved in casing gun assemblies than the through-tubing units. In particular, the through-tubing units presently in use may contain the same amount of charge as casing guns but have not been able to penetrate as deeply into the formation owing to their wider cone angle and limitations in overall size imposed by the inner concentric tubing strings through which they are deployed. The through-tubing devices are principally employed where high pressure and well conditions are such that perforating with casing gun assemblies is not practical. Typical of the casing gun types of perforating assemblies are those disclosed in prior U.S. Pat. No. 4,253,523 and prior pending patent application, U.S. Ser. No. 299,479, filed Sept. 4, 1981, now U.S. Pat. No. 4,467,878 for SHAPED CHARGE AND CARRIER ASSEMBLY THEREFOR.
It is now proposed to provide a through-tubing perforating assembly capable of achieving much greater penetration and specifically in such a way as to be able to employ standard casing gun charges possessing the desired penetrating configuration while withstanding high pressure conditions; yet can be passed through relatively small diameter tubing to the desired zone or formation to be perforated.
Representative U.S. Letter Patents disclosing through-tubing perforating apparatus are U.S. Pat. Nos. 2,746,828 to H. H. Rachford, Jr.; 3,207,072 to J. R. Holden; 3,234,875 to E. O. Tolson; 3,238,872 to L. Zernow et al; 3,244,101 and 3,268,016 to W. T. Bell; 3,259,064 to N. G. Owens; 3,302,567 to A. A. Venghiattis; 3,419,070 to E. A. Ernst; 3,517,745 to G. O. Suman, Jr.; and 3,627,045 to M. P. Lebourg.